Simultaneous plural spacing acoustical logging



sIMULTANEoUs PLURAL SPACING AcoUsTcAr. LOGGING Filed sept. 28, 1959 Sept V3, 19.63 K. D. SAVAGE ETAL 2 Sheets-Sheet 1 3,102,992 SIMULTANEOUS PLURAL SPACING ACOUSTICAL LOGGING Filed sept. 28, 1959 Sept. 3, 1963 K. D. SAVAGE ETAL 2 Sheets-Sheet 2 United States Patent O 3,102,992 SIMULTANEUUS PLURAL SPACING ACUSTICAL LGGlNG Kerry D. Savage, Houston, Roy P. Mazzagatti, Bellaire, and Gerhard Herzog, Houston, Tex., assignors to Texaco lne., New York, NX., a corporation of Delaware Filed Sept. 28, 1959, Ser. No. 842,923

. 12 Claims. (Cl. 34E-1S) v This invention relates to the determination of an acoustical property of subsurface strata which has been traversed by :a borehole, and more particularly to a well logging system which provides a plurality of acoustical velocity logs simultaneously.

In the present state of the art of :acoustical velocity well logging acoustical velocity logs of formations surrounding a *borehole are being provided by the use of a one receiver system, that is, a system having one acoustical transmitting transducer 'and one acoustical receiving transducer, or by a two receiver system, that is, a system having one acoustical transmitting transducer and two acoustical receiving transducers, as disclosed in a copending application Serial No. 574,844, Itiled March 29, 1956, of R. J. Loofbourrow which issued on. April 5, 1960, las U.S. Patent 2,931,455, entitled Acoustic Logging of Wells, The ydifference in arrival times of lan `acoustic pulse at two of the Vspaced apart transducers isV measured. The spacingsbetween the transducers being a constant, the measurement of time of travel of -an acoustic pulse from one transducer to 'another can be converted into and recorded as the velocity of the acoustic wave or pulse` and plotting total time-of-travelof the acoustic pulse with `deptlrfor seismic calculations. In many instances, the longer spacing is found to be more desirable `or satisfactory for correlating between wells. Accordingly, it

can be seen that la long spacing between receivers is more i desirable for many purposes.

However, considerable experience in log ing boreholes with acoustical velocity loggingsystems has shown that velocity logs with a short spacing between transducers, say, on the order of one foot or even less, provide very detailed information of the subsurface formation. Since the velocity measurement is restricted to the interval between two transducers, and since that interval `can be as short as a few inches, Ithe systems employing short spaced transducers can 'very accurately locate boundaries of beds, even of thin beds. Accordingly, it can be seen that an acoustical velocity well logging system which can provide logs from both short spaced and long spaced transducers is very desirable.

In accordance with the present invention, lanv acoustical well logging system having several transducers is provided which produces a plurality of acoustical logs. More particularly, the present invention provides a system wherein a plurality of acoustical logs. is produced simultaneously. The system of the present invention includes an elongated tool whichcontains one acoustic transmitter located at `different distances from the transmitter.

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For a better understanding of the invention, reference may be had to the accompanying drawing in which:

FIG. l is a circuit diagram primarily in block form illustrati-ng the subsurface or borehole equipment in accordance with the present invention including a sectional view of the earth and parts of the apparatus disposed in a borehole therein, and

FIG. 2 is a `circuit `diagram primarily in block form 'illustrating the surface equipment of the system of the present invention including a sectional view of the earth and parts of the apparatus disposed in a borehole therein.

As stated above, the acoustical velocity through subsurface formations is determined by measuring the time of travel of an acoustic pulse through the subsurface formations between two spaced apart transducers. It can be seen that Jthe time of travel may be measured `between an acoustical transmitting transducer and an acoustical receiving transducer spaced 'apart a known distance. Alternatively, the velocity of a sound wave passing through a .subsurface formation may 4be determined by measuring the time of travel Iof the sound Wave between two spaced apart receiving transducers. The present invention, as illustrated in FIGS. ll and 2 of the drawing, provides an acoustical well loggingsystem. wherein the time of travel is determined between a transmitting transducer and a receiving transducer and between at least two spaced apart receiving transducers. However, in the interest of accuracy, the time of travel of an acoustic pulse is measured preferably ybetween two receiving transducers, since in the one receiver method the time of travel ofthe acoustic pulse through the borehole fluid from the transmitting transducer to theformation and again from the lformation to the receiving transducer provides inaccuracies which cannot be readily corrected. These inaccuracies are substantially eliminated when a two receiver system is used since the time of travel through the borehole fluid to each of the two receivers can be considered as being equal.

Referring in more detail to FIG. l of the drawing, a borehole l0 containing a. borehole liquid, which may be conventionally used borehole drilling mud, is shown traversing a plurality of subsurface formations 12, 14 and` 16, in which formations it is desired to determine the acoustical velocity. Disposed within the borehole is an exploring unit or elongated tool 13 supported by a conventional 5/16 single conductor borehole cable 20. The single conductor cable `2li includes a central conductor 22 generally composed of copper or other highly conductive i metal and `an outer sheath 24 made of steel strands having a strength suiflcient to support the exploring unit 18 and its 'own weight in the borehole. The exploring unit 1S has `an acoustical section 26 in the lower end thereof in which an acoustic pulse transmitting transducer 23, a first receiving transducer 30, a second receiving transducer 32 and a third receiving transducer 3d are contained. Each of the transducersis preferably of the lead zirconate titanate type or of the barium titanate type.` The walls i and the interior of the acoustical section 26 of the exploring unit 18' are made lof a material in which the acoustical velocity of sound is not greater than the acoustic velocity of sound passing through the duid in the borehole 1G, preferably a material in which velocities are less than 5,000Vfeet per second and which can withstand the high temperatures 'and pressures encountered in a borehole, for example, a rubber-like material such as neoprene. The upper section of the l:exploring unit 18 is the electronic section 36 wherein the exploring unit electronic components are housed.

The electronic section 36 houses a timer unit 38 which may be any desirable oscillator producing pulses preferably lat a constant repetition rate of frequency, for eX- ample, at 20 pulses per second. `An acoustical pulse trans-` sive to a pulse from the differentiator. The output from the first delayed gate generator is coupled to a first gated trigger generator 44.

The first receivingtransducer 30 in the acoustical section 26 of the exploring unit 18 is coupled to a first high-pass filter 46 which preferably has a cut-off frequency of approximately kilocycles. A conventional amplifier and clipper 48 is connected to the output of the first filter 46. The output voltage from the first amplifier and clipper 48 is applied to tan input `of the first gated trigger generator 44. The first gated trigger generator 44 may conveniently be a dual control coincidence thyratron having two control grids, one having applied thereto the positive voltage from the output of the first delayed gate generator 42 and the other control grid having applied thereto the pulse from the first receiver 30 which passes through the first filter 46 and the first amplifier and clipper 48. The first gated trigger generator 44 is coupled to an electric pulse collecting circuit 50 through a first blocking diode 52, the pulse collecting circuit 50 being preferably a dual` cathode follower 55 having a first ytriode section 54 and a second triode section 56, a common cathode resistor 58, a

first grid resistor 60 connected to the control grid of the first triode section 54 and a second grid resistor 62 connected to the control grid of the second triode section 56. The output ofthe blocking diode 52 is connected to the control grid lof the first triodesect-ion 54.

An output voltage from the first gated trigger generator 44 is also applied 4to a second delayed gate generator 64, which may be similar to the first delayed gate generator 42, to produce at its output a positive square Wave.

Coupled to the output of the second receiving transducer 32 is a second filter 66 which is also preferably a high-pass filter having a cut-off frequency of approximately 5 kilocycles per second. Asecond amplifier and clipper 68 is connected to the output of the second filter 66. The output of the second amplifier and clipper 68 is connected to the input of a second gated trigger generator 70 which may be similar to the first gated trigger generator generator 74 which may be similar to the first and second delayed gate generators 42 and 64.

Coupled to the output ofthe third receiving transducer 34 is a ,third filter 76 which is also preferably a high-pass filter having a cut-off frequency of approximately 5 Akilocycles per second. A third amplifier and clipper 78 couples the output lof the third filter 76 to an input of a third gated trigger generator 80. The output from the third delayed gate generator 74 is also connectedvto an4 input of the third gated trigger generator 80. The third gated trigger generator is preferably similar to the first and second gated trigger generators 44 and 70. The output from the third gated trigger generator 80 is coupled to the pulse collecting circuit through a third blocking diode 82 which is connected to the control grid of the first triode section 54 ofthe dual cathode follower 55.

An output from the timer unit 38 is also connected to the pulse collectingcircuit 50 through a fourth blockl ing diode 84, which diode is connected to the control grid of the second triode section 56 of the dual cathode follower 55.

rPhe cat-hodes of the dual cathode lfol-lower 55 of the pulse collecting circuit 50 are connected to lthe control grid of a lhydrogen thyratron 86 of a cable pulsing circuit 85 through a coupling capacitor 88. The control grid of the hydrogen thyratron 86 is also connected to a negative tdirect current potential through an inductor 90. An energy storing network 92 which includes a first capacitor 94, a second capacitor 96 and a coil 98 is connected between ground and the anode of the hydrogen thyratron 86, which anode is alsok connected through a `resistor 100 to the B-lsupply. 'Phe energy storing network 92 may be, as is well known, an appropriate length of coaxial cable. A cathode resistor 102 is connected-between the cathode of the hydrogen thy-ratron 86 and ground. A coupling capacitor 104 is connected between the cathode of the hydrogen thyra.- tron `86 and the central conductor 22 of the single conductor cable 20. A boreholepower supplyy 106 is also connected to the central conductor 22 of the vsingle conductor cable 20 through a filter network `108 which includes a capacitor 110 connected Ibetween borehole power supply 106 and 'ground and an inductor 112 which is connected between the borehole power supply 106 and the central conductor 22 of the single conductor cable 20. Y

The surface Iequipment tof the acoustical velocity well logging system of the present invention is `illustrated in PIG. 2. As shown in this figure the single conductor cable 20 passes over a cable measuring device 114. The central conductor of the single conductor cable 20 is connected to a filter 116 which is suitable for sepa rating the borehole power energy from the acoustic velocity intelligence which is being transmitted through the same conductor, that is, the central conductor 22. The power necessary to energize the exploring unit is derived from the 60 cycle per second power source 118, which is connected to the filter 11-6. Fllhe 60 cycle per second power source 118 also isv connected to the surface power supply `120.

`The filter 116 also is connected to an amplifier and shaper 122. The output of theramplifier and Shaper 122 is connected to a first trigger thyratron circuit 124 which may include lay thyrat-ron tube 126 `having a cathode resistor 128, an anode resistor 130 and a storage capacitor 132 connected between the anode of the thy-ratron 126 and ground. The cathode of the thyratron 126 isl connected to a first time measuring circuit which includes a first bi-ntable multivibrator 134 to which is connected a first sawtooth tgenerator 136 followed by a first peak reading vacuum tube voltmeter 138. I'he output from the first peak reading vacuum tube voltrneter 138 is applied to a first recorder 140 through a first ldirect current voltage amplifier 142.

'l'he output from the amplifier and Shaper 122 is also applied to a first first-pulse deletion circuit 144. The first-pulse deletion circuit 144 comprises a convention-al one shot multivibrator 146 having a first triode 148 and a second triode 150. The amplifier and Shaper 122 is connected, more particularly, to the control grid of the first triode 148 of the first-pulse deletion circuit 144 through a coupling resistor 152. rlhe anode of fthe second triode 150 of the one-shot multivibrator 146 is con'- nected through a first resistor 154 connected in seriesv with the parallel combination of a .second resistor 156 and a capacitor 158 to a B- supply. Also connected to the output of the amplifier and Shaper 122 is a'first load resistor 160l con-nected thereto through a first coupling capacitor 162. A silicon diode 164, which is preferably a l-N-646, is connected between the first load resistor 160. and the common point between the firstresistor 154 and the second lresistor 156. A second load resistor 16,6 is connected between the common point of the first coupling capacitor lr62 and the first load resistor le@ and ground. A second coupling capacitor ldd is connected between the common point of the first load resistor 16@ and the silicon diode 164 and a grid resistor l''ll. The Igrid resistor 170* is connected between the control grid of a cathode follower 72 and a negative direct current potential lor bias source. The anode `of the cathode follower 172 is connected directly to the B+ supply and the cathode of the cathode follower 172 is connected through a cathode resistor 171i to ground. The cathode of fthe cathode follower i172 is connected to a second trigger thyratron 17o which may be similar to the first trigger thyratron 124. The output of the second trigger thyratron 17e is connected to an input of the first bi-stable multivibrator 134 of the first time measuring circuit.

The output of the second trigger thyratron 176 is also connected to second and fthird time measuring circuits which may be similar to the first time measuring circuit. The second time measuring circuit includes the second bi-stable multivibrator l, a second sawtooth ,generator 18d, a second peak reading vacuum tube voltmeter 132, a second direct current amplnier ld and a second recorder ldd. The third time measuring circuit includes -a third bi-stable multivibrator 153, a third sawtooth generator 190, a third peak reading vacuum tube voltmeter 192, la third direct current amplifier 194 and a third recorder 1%.

The cathode of the cathode follower 172 also is connected to a second first-pulse deletion circuit 19t-i which is similar to the first first-pulse deletion circu-it ldd. The output from the second first-pulse deletion circuit i198` is connected [to a third trigger thyratron Zilli which is similar to the first and second trigger thyratrons 124i and T76. The output from the third trigger thyratron Zilli is applied to an input of the second bi-stable multivibraltor i7@ of the second time measuring circuit. The output from the second first-pulse deletion circuit E98 also is connected to a third first-pulse deletion circuit 25312, the loutput of which is connected to an input of the third bi-stable multivibrator 138.

ln the operation of the acoustical velocity well logging system of the present invention, an electric pulse tu produced by the timer unit 38 is applied to the acoustic transmitter puiser dit which produces a sharp high-energy electric pulse for actuating the acoustical transmitting transducer 28. The electric pulse to `from the timer unit 38 is simultaneously applied through the blocking diode d4 to the control grid of the second triode section 56 of the dual cathode follower 55 to produce a pulse tu across the cathode resistor 58 of the dual cathode follower 5'5. rIlle electric pulse zo from the timer unit 38 is also simultaneously 'applied to the first delayed gate generator 42 which, after a delay of approximately 100 microseconds, produces a positive square wave having a duration of approximately 600 microseconds which is applied to the first lgated trigger generator df to place this generator in condition to operate upon the receipt therein or" a pulse from the first amplifier land clipper 4S.

The acoustic pulse To produced at the transmitting transducer 23 travels through the borehole fluid into the subsurface formation 14 where .a portion of it is refracted through the formation ldtowaud the first, second and third receiving transducers Sil, 32 and 34. A portion of the refuacted acoustic pulse or wave reenters the borehole fiuid to strike the first receiving transducer 3d and at a later time depending upon the acoustic properties of the .formation 14 another portion of the refracted wave reenters the borehole fluid to strike the second receiving transducer 32 and at a still later time still another portion of `the refracted Wave reenters the borehole fluid to strilce the third receiving transducer 34. The voltage developed by the first receiving transducer 30 corresponding to the acoustic energy received thereby is applied to the first amplifier and clipper 48 through the first filter d d6. The pulse from the output of the first. amplifier and clipper t8 is applied to the Ifirst `gated trigger generator All to produce at the output thereof a single pulse t1 which is applied to the control grid of the first triode section 54 of the dual lcathode follower 55 setting up the Vpulse t1 across the cathode resistor 58. It should be understood that due to the ringing of the transmitting transducer 28 a wave train rather than a single: pulse will be received lat the receivers 3f), 32 and 3d. in order to produce a single pulse t1 indicative of the instant at which the first wave of the wave train reaches the first receiving transducer Sli, the first gated trigger generator is designed so that the first wave of the wave train triggers the generator de to produce the pulse t1 and generator 44 remains unresponsive to the remaining waves of the wave train. This may be readily accomplished by providing an eneugy storage network which discharges at the instant of arrival of the first wave Vof the wave train but does not become rechargeduntil after the wave train has passed.

A. portion of the voltage developed across the output of the first gated trigger generator 44 is applied to the second delayed gate generator ed which after a delay of approximately 30 microseconds produces la positive pulse or wave having a duration of approximately 200 microseconds at its output. The 200 microseeond positive pulse is applied to the second :gated trigger lgenerator 70 to place the second gated trigger generator 7d in `a condition to operate when a pulse is received therein from the second yamplifier and clipper 6d.

The voltage wave train developed across the second receiving transducer 32 corresponding to the acoustic energy received thereby is applied to the second `amplifier and clipper 68 through the second filter 66. The first wave of the wiave train from the output of the second amplider and clipper e8 is yapplied to the second gated trigger generator 7@ to produce at the output thereof an electric pulse t2 indicative of the instant of arrival of the acoustic energy at the second receiving tuansducer 32. The electrical pulse t2 is applied through the second blocking diode F2 to the control grid of the second triode section Se of the dual cathode follower 55 to produce across the `cathode resistor S8 the electric pulse t2.

The electrical pulse t2 produced at the output of the second gated trigger generator 7d is also applied to the third delayed gate generator 74 which after a delay of approximately 60 ymicroseconds produces a positive pulse or Wave having a duration of approximately 400'microseconds at its output. The 400l microsecond positive pulse from the third delayed gate generator 74 is applied to the third 'gated trigger generator 3f) to place this generator in a condition to operate upon the arrival of a pulse from the third `amplifier `and `clipper '73.

The voltage wave train developed across the third receiving transducer 34 corresponding to the acoustic energy received thereby is applied to the third amplifier and clipper 75 through the third filter 76. The first wave of the wave train from the output of the third amplifier and Iclipper 7S operates the third gated trigger generator Sli to produce at the output thereof `a fourth electrical pulse t3 which is applied through the third blocking di- -ode 82 to the control ygrid of the first triode section 54 of the dual cathode fol-lower S5 to produce the electric pulse f3 across the cathode resistor 58.

Accordingly, it can be seen that the four pulses to, t1, t2 an'd t3, each of which are indicative of the instant at which a portion of energy of au acoustic pulse was present at the respective transducers, are produced across the cathode resistor '58 of the du-al cathode follower S5 of the pulse collecting circuit Si). The four pulses produced across the cathode resistor 53 are then .applied to the control grid of the hydrogen thyratron 86 of the cable pulsing circuit S5 through the coupling capacitor 88. The pulse to first fires the hydrogen thyratron 86 discharging the '7 energy stored in the storage network 92 to produce a high-amplitude short-duration pulse across the cathode resistor 102 of the hydrogen thyratron 36. As the energy from the storage network 92 is discharged, the hydrogen thyratron 86 will extinguish `and the storage network will be rapidly recharged by the energy from the B+ supplyv through the charging resistor 1011 so as to await the arrival of the second pulse t1. The choke 90 and the negative directpourrent voltage applied through the choke 911 to the control grid ofthe hydrogen thyratron 86 are provided so as to rapidly deionize the thyratron 86. The cable pulsing cir-cuit responds to the subsequent pulses, that is, pulses t1, t2 and t3, in a similar manner to produce across the cathode resistor 102 the four pulses t0, t1, t2 and t3. These four pulses are then applied to the central conductor 22 of the single conductor cable 20 through the coupling capacitor 104.

It should be ,understood that the B-lsupply, the negative direct current or bias voltage and the lament voltage for the circuits contained in the exploring unit 18 are all derived from the borehole power supply 106 which is illustrated merely in block form since it may be of the conventional type and would unduly complicate the drawing if illustrated in detail. The borehole power supply 106 is energized by a 60 cycle per second power source 118 located at the surface of the earth. The 60 cycle energy is fed from the cable 211 to the borehole power supply 106 through the inductor 112. The inductor 112 and the capacitor 111i are provided to prevent the pulses to, t1, l2 and t3 from entering into the borehole power supply 1116. The voltage from the 60 cycle power source 118 is 280 volts so as to provide 240 volts at the input of the power supply 1116 since a 40 volt drop in the cable 26 was encountered. However, as understood by those skilled in the art, this voltage may be varied depending upon the circuits or elements used in the acoustical well logging system. The surface power supply 12@ which is also energized by the 60 cycle per second power supply 118 supplies the B-, B+, negative direct current or bias potential and filament voltage to the surface equipment. Since the surface power source may also be a conventional power supply, details .thereof have not been disclosed. The 60 cycle per second voltage from the power source 118 is applied to the central conductor 22 of the single conductor cable 20 through the filter 116.

The four electric pulses to, t1, t2 and t3 transmitted up the single conductor cable are applied through filter 116 to the amplifier and Shaper 122 which produces at its output sharp pulses to, ll, f2 and 13 of substantially equal amplitude. These pulses correspond with the pulses produced at the cathode of the hydrogen thyratron 86 of the cable pulsing circuit except that they are displaced from the pulses to, l1, t2 and t3 produced at the hydrogen thyratron 86 by an amount equal to the time delay in transmission through the single conductor cable. This time delay may be in the order of 50 microseconds. However, since each of the four pulses are transmitted by the same conductor in the cable 2.1i, they are delayed by the same amount, and, therefore, the time interval between the pulses to and t1 is the same as that between to and t1, and the time interval between tl `and I2 is the same as that between t1 and l?, etc. The four pulses 10, t'l, t2 and tg from the amplifier and Shaper 122 are applied to the control grid of the first trigger thyratron 124. The first pulse, that is, tU, triggers the thyratron 126 which discharges the energy stored in the storage capacitor 132 through the cathode resistor 12S to produce the pulse to across the resistor 128. Since the charge resistor 131i has a high resistance value, the storage capacitor 132 cannot be immediately recharged and, therefore, the subsequent pulses tl, t'2, and t3 will not be capable of triggering thyratron 1216. The values of the charging resistor 131? and the storage capacitor 132 are such that the storage d capacitor 132 will be sufficiently recharged to again discharge through the thyratron 126 when the next series of pulses to, tl, t'2 and 23 are applied to the grid of the thyratron 126.

The four pulses to, f1', t2 and t3 from the amplier and Shaper 122 also are applied to the control grid of the first triode 143 of the one shot multivibrator 146 through the grid resistor 152. The first triode section 143 is normally in a non-conducting condition and the second triode section 151i of the one shot multivibrator is normally in a conducting condition. When the first pulse, that it, pulse to, is applied to the grid of the rst triode section 148 the first triode section is placed in a conducting condition and the second triode section then becomes Ynonconductive.V Thus, the voltage Vat the anode of the second triode section 15@ begins to increase to form a positive-going pulse. The time constant of the multivibrator 146 is such that the positivegoing pulse at the anode of the second triode section 150l has a duration of approximately 1400 microseconds. The pulse to from the amplifier and Shaper 122 also is applied through the coupling capacitor 162 to the first load resistor 161) and then to ground through the normally conducting silicon diode 164, the capacitor 15S and the B- supply. The silicon diode 164 and the capacitor 158 are very low impedances for the pulse to and, therefore, the voltage at the common point between the load resistor 160 and the silicon diode 164 is of a very small value and not sufficient to overcome the negative bias on the control grid of the cathode follower 172. Consequently, a pulse to is not produced across the cathode resistor 174 of the cathode follower 172. At the time that the subsequent pulse, that is pulse 11, from the amplifier and Shaper 122 is applied to the first load resistor 160, the silicon diode 164 is rendered non-conductive by the positive pulse from the anode of the second triode section 150 of the one shot multi- Vibrator 146. Accordingly, this pulse tl and pulses 12 and 13 will be passed through the coupling capacitor 168 to the control grid of the cathode follower 1.72 to produce corresponding voltages across the cathode ,resistor 174. The second load resistor 166 is provided to complete the direct current path for the silicon diode 164 while that diode is conducting.

The pulses t1, tz and t3 now being separated from the pulse to in the first first-pulse deletion circuit 144 can be applied to the second trigger thyratron circuit 176. Since the second trigger thyratron circuit 176 is similar to the first trigger thyratron circuit 124 the first pulse applied thereto, that is, pulse tl, will be produced at the output thereof While the pulses t'2 and t3 will be prevented from passing through the second thyratron 1716.

Since the pulses to 'and t'l have been separated from the series of pulses t'o, ll, tz and t3, it can be readily seen that these two pulses may be applied to a time measuring circuit so as to determine the time interval required for the acoustic pulse to tlnavel between the acoustical transimitting transducer 28 and the first receiving transducer Siti. As illustrated in FIG. 2 of -the `drawing the pulse to at the cathode of the thyratron 126 of the 'first trigger thyratron circuit 124 is Iapplied to the first bi-stable multivibrator 134 to produce a negativesgoing pulse or waive at the output thereof. The negativeegoing `wave `at the first bi-stable multivibrator 134 is terminated by the [application thereto fof the pulse t'l from the second trigger thyratron 176. The negative-going pulse at the output of the first multivibrator 134 which has a duration equal to the time of travel of the acousticl pulse To between the transmitting tnansducer 28 and the first receiving transducer 30 is applied to the first sawtooth generator 136 to produce Ia. sawtooth wave having a maximum amplitude which is proportional to the time of travel of the acoustic pulse between transmitting tnansducer 23 `and the receiving transducer 30. The first peak reading vacuum and 32, the pulse 1'1 is applied from the second trigger.

thyratron circuit T76 to ythe second `bi-stable multivibrator 178 of the second time measuring circuit to initiate a negative-going Wave at the output of themultivibrator 178. The pulse f2, lbeing needed to terminate this negative-going Wave, is provided by applying the pulse f1, f2 and 1'3 from the voutput of the Ifirst firsupulse deletion circuit to the second rst-puise deletion circuit "i193 which passes only pulses lz and t3 in a manner similar to `that described in connection with the first iirstpulse deletion circuit M4. The pulses tz and ts are then applied to the third trigger thyratron circuit Zilli at the output of Which only the pulse f2 appears. The negative-going Wave at the output of the second multivibrator i173, thus has a time duration equal to the time or" travel oftheacoustic pulse To between the first receiving transducer @il and the second receiving transducer 32. The negative pulse at the output of the second ibi-stable multivibrator 17S is then applied to `the second sawtoot-h generator 18d which produces a sau/tooth voltage having a peak value vproportional to the time interval between pulse tl and f2.

The second peak reading vacuum tube voltmeter 132 and the second direct current voltage amplifier ld are used to provide a idirect current voltage indicative of the time interval between t'l and t'2 which may be recorded in the second recorder 186, in la manner similar to lthat described in connection with the first time measuring circuit.

To determine the travel time of the acoustic pulse between the first receiving transducer @il and the third re-l ceiving transducer 34, the pulses tl and t3 are applied to the third *bi-stabile multivibrator idd. arated from the pulse 12 at the output of the second iirstpulse deletion ycircuit 198 by applying these pulses, t'2 and t3, to the third first-pulse deletion circuit Zil. "Thus, the time of travel of the acoustic pulse lbetween the iirst receiving transducer and the third receiving transducer 3tl-` may `be readily recorded lby the third time measuring v circuit "which includes the third bi-stable multivibrator 188, thethird sau/toothV generator i943, the third peak reading vacuum tube voltmeter E92, the third direct current voltage ampliiier 1% and the third recorder i196.

It can be seen that in the -acoustical velocity Well logging system fof the present invention, pulses tu, t1, t2 and t3 representing instances of time'at which an acoustic pulse T0 is present at a particular transducer are produced in an exploring unit, are collected therein land transmitted through ra single channel to the surface of the earth where `they `are separated and `applied to selected time measuring circuits. It should be understood that additional time measuring circuits may be utilized at the surface to accommodate any desired combination of the pulses transmitted to the earths surface. Furthermore, it should be understood that additional receiving transducers may =be added to the exploring unit 118 and that the spacing of the receiving transducers from each other 'and from the produces simultaneously a plurality of acoustical logs of subsurface formations traversed by a borehoe including both single receiver and two-receiver logs.A Moreover,` the plurality of logs are produced simultaneously with the lil use of -a borehole cable which has only a single insulated conductor.

Obviously, many modifica-tions .and variations of the invention as hereinbefore set forth, may be made Without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

' "We claim:

l. An acoustical velocity Well logging system `comprising an elongated tool adapted to be passed through the borehole of a Well, said toolhaving first, second and third transducers positioned in iiXed spaced apart relationship in said tool, said transducers being mounted for acoustic communication with material including a subsurface formation opposite said tool, means for transmitting acoustic pulses at predetermined time intervals through a subsurface formation opposite said tool, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, means for producing a third electric .pulse upon the arrival of said given acoustic pulse at said third transducer, a single insulated conductor, means for applying said iirst, second and thirdV electric pulses to one end ot` said single conductor, first and second time measuring circuits, meanscoupled to the other end of said single insulated conductor for applying a different pair selected from said first, second and third electric pulses to `each of said time measuring circuits so as to measure the time interval between the respective pulses of the selected pairs of said electric pulses.

2. A; system for determining acoustic velocities through a subsurface formation traversed by a borehole comprising means for transmitting an acoustic pulse through the subsurface formation from first to second to` -third spaced apart points in the borehole, means for producing first, second, and third electric pulses in predetermined timerelationship With said acoustic pulse at said first, second and third points, respectively, a single transmission line,

'means for applying said first, second and third electric pulsesl to oneend `of said Vsingle transmission line, and means operatively coupled to the opposite end of said transmission line for selectively separating said lirst,

' second and third electric lpulses into at least two different pairs of electric pulses, and means operatively coupled to vsaid pulse yseparating means for measuring the time interval between the respective electric pulses of said different pairs selected from said iirst, second and third electric pulses. Y

v3.15m acoustical velocity Well logging system comprising an elongated tool adapted to be passed through theborehole of the Well, said tool having iirst, second and third transducers positioned in fixed spaced apart relationship in said tool, means for transmitting an acoustic pulse atpredetermined time intervals through the .subsurface formation opposite said elongated tool, means `for producing a iirst electric pulse at the yoccurrence of a given one of said acoustic pulses at sai-dfirst transducer, means for producing a second electric pulse on the arrival of said given acoustic pulse at said second transducer, means for producing a third electric pulse upon the arrival kof said given acoustic pulse at` said third transducer, a single transmission line, a cable pulsing circuit coupled to said transmission line, said cable pulsing circuit being operatively associated with said means for producing said first, second and third electric pulses such that said cable pulsing circuit is responsive to each of said iirst, second and third electric pulses, said cable pulsing circuit including a pulse forming network and a fast-acting swithvfor applying high-power, short-duration pulses to one end of said transmission line, first and second time measuring circuits, means for deriving from said transmission line la first pair of said firstsecond and third lil electric pulses and for applying said first pair of electric pulses to said first time measuring circuit and for deriving from said transmission line a second pair of said first, second and third electric pulses and for applying said second pair of electric pulses to said second time measuring circuit. f

'4. An acoustical velocity Well logging system comprising an elongated tool adapted -to be passed through the borehole of a well, said tool having first, second and third transducers positioned in fixed spaced apart relationship in said tool, said transducers being mounted for acoustic communication with material including a subsurface formation opposite said tool, means for transthrough a subsurface formation opposite said transducers,

means for vproducing a first electric pulse at the occur-l rence of a given one of acoustic pulses at said first transducer, means for producing a` second electric pulse upon the arrival of said given acoustic pulse at said second transducer, means for producing a third electric pulse on the arrival of said given acoustic pulse at said third transducer, a single transmission line, a cable pulsing circuit for applying high-power, short-duration pulses to one end of said transmission line, means for collecting said rst, second and third pulses and for applying them to the input of said cable pulsing circuit, a plurality of time measuring circuits and means coupled t the other end of said single transmission line including a separate circuit for deriving each of said first,` second and third electric pulses for applying a first pair of said electric pulses to one of said plurality of time measuring circuits and a second pairl of said electric pulses to another of said plurality of measuring circuits.

5. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the borehole of a well, said tool having first, second and third transducers positioned in fixed spaced apart relationship in said tool, said transducers being mounted for acoustic communication with material including a subsurface formation opposite said tool, means for transmitting an acoustic pulse at predetermined time intervals through a subsurface formation opposite said tool, means for producing a first electric pulse at the occurrence of a given oneof said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse Yat said second transducer, means for producing a third electric pulse upon the arrivalfof said given acoustic pulse at said third transducer, a single transmission line, means operatively associated with said means for producing said first, second and third electric pulses and responsive to said electric pulses `for producing high-power, short-duration pulses, means for applying the high-power, short-duration pulses to one end of said transmission line, first and second time measuring circuits, means coupled to the opposite end of said transmission line for applying a first pair of said short-duration electric pulses to said first time measuring circuit and for applying a second pair of said electr-ic pulses to said second time measuring circuit, an electric power source, first filter means for connecting said power source to said opposite end of said transmission line and for separating said first, second and third electric pulses from the energy derived from said source, means disposed at said one end of said second transmission line for receiving the energy from said power source, and

second, filtering means disposed between said energy receiving means and said single transmission line for preventing said first, second and third electric pulses from entering said energy receiving means.

6. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the borehole of a well, said tool having first, second and third transducers positioned in fixed spaced apart relationship in said tool, said transducers being mounted for acoustic communication with material including a sub- 'arrival of said given acoustic pulse at said second transducer, means for producing a third electric kpulse upon the arrival of said given acousticv pulse at said `third transducer, a single transmission line, means for applying said electric pulses to one end of said single transmission line, first and second time measuring circuits each including a scale-of-two circuit, means coupled to the other end of said single transmission line for applying a rst pair of said electric pulses to said first time measuring circuit and for applying a second pair of said electric pulses to said second time measuring circuit.

7. An acoustical velocity well logging system compris-` ing an elongated tool adapted to be passed through the borehole of a well, said tool having a transmitting transducer and first, second and third receiving transducers, said transducers being positioned longitudinally in fixed spaced apart relationship in said tool, means for producing a first electric pulse for actuating said 'transmitting transducer to produce an acoustic pulse for passage through a subsurface formation opposite said tool, means for collecting electric pulses, means for applying said first electric pulse to said pulse collecting means, means for producing a second electric pulse upon thearrival of said acoustic pulses at said` first receiving transducer,

means for applying said second electric pulses to said pulse collecting means, means for producing a third electric pulse upon the arrival of said acoustic pulse at said A second receiving transducenvmeans for applying said third electric pulse to said pulse collecting means, meansl Y for `producing a fourth electric pulse upon the arrival of said acoustic pulse at said third receiving transducer, means for applying said fourth electric pulse to said pulse collecting means, a single transmission line, means re sponsive to said electric pulses for producinghigh-power, short-duration electric pulses, means for applying said high-power, short-duration pulsesl to one end of said.

second time measuring circuits, means Ifor applying said second and third short-duration pulses to said first time measuring circuit and means for applying said second and fourth short-duration pulses to said second time measuring circuitfor measuring the time of travel of said given acoustic pulsegbetween said first yand second receiving vtransducers and between said first and third receiving transducers, respectively. i v

8. A acoustical velocity Well logging system comprising an elongated tool adapted to be passed through the borehole of a well, said tool having t'rst, second vand third tnansducers positioned in kfixed spaced apart relationship in said tool, said transducers being mounted for acoustic communication with material including a subsurface formation opposite said tool, means for transmitting acoustic pulses at predetermined time intervals through a subsurface formation opposite said tool, means for producing a first electric pulse at the occurrence of a given ione of said acoustic pulses at said first transducer, meansfor producing a second electric pulse upon the arrival of said given acoustic pulse at said second transducer, means for propulses therein, time measuring means for measuring the interval between a pair of electric pulses, means operatively coupled to the opposite end of said transmission line lfor separating each of the first, Isecond and third electric pulses from said train of pulses and for applying a selected plurality of pairs of said separated pulses to said time measuring means to measure the time interval between the respective pulses of each of the plurality of pairs of pulses.

9. An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the borehole of a Well, said tool having first, secondrand third transducers positioned in t'ixed :spaced apart relationship in said tool, said transducers being mounted for acoustic communication with material including a subsurface formation opposite said tool, means for transmitting acoustic pulses Iat predetermined time intervals through a subsurface formation opposite said tool, means for producing a first electric pulse at the occurrence of a given one of said acoustic pulses at said first transducer, means for producing a second electric pulse upon the arrival of said given acoustic pulse `at said second transducer, means for producing a third electric pulse upon the arrival of said given acoustic pulse at said third transducer, a single transmission line, means for applying said electric pulses to one end of said transmission line to form therein a train of pulses, a plurality of time measuring circuits, means for separating each of the pulses from said train of pulses and means for applying a different pair of the separated pulses to each of said plurality of time measuring circuits.

l0. An acoustical velocity well logging system as set forth in claim 9 wherein said pulse separating means includes a plurality of circuits for deleting a -first pulse of a series of pulses applied thereto and a plurality of circuits for passing only the first pulse of a series of pulses applied thereto.

l1. An acoustical velocity well logging system as set forth in claim 10 wherein each of said pulse deletion circuits includes Va diode anda one shot multivibrator having the output applied to said diode to render said diode inoperative for a predetermined portion of time following the application thereto of a iirst pulse of a series of pulses and wherein said first pulse passing circuit includes a thyratron adapted to be discharged only once upon the arrival thereat of a series of pulses during a predetermined interval of time.

12. `An acoustical velocity well logging system comprising an elongated tool adapted to be passed through the borehole of a well, said tool having an acoustical transmitting transducer and iirst, second and third-receiving lli transducers, said transducers ybeing positioned longitudinally in Xed spaced apart relationship in said tool, means for producing a rst electric pulse for actuating said transmitting transducer to produce an acoustic pulse for passage through a subsurface formation opposite said tool, means for producing a second electric pulse upon the arrival of saidacoustic pulse at said first receiving transducer, means for producing a third electric pulse upon the arrival of said acoustic pulse atv said second receiving transducer, means for producing la fourth electric pulse upon the arrival of said acoustic pulse at said third receiving transducer, a single transmission line, means for applying said first, second, third and fourth electric pulses to one end of said transmission line, tiret, second and third time measuring circuits, each of said time measuring circuits including a bi-stable multivibrator and means coupled to the opposite end of said transmission line for applying selected pairs of said electric pulses to said time measuring circuits, said means for applying said electric pairs of said electric pulses including first means coupled to the opposite end of said single transmission line for passing only said first electric pulse, the output of said rst means being applied to the `bi-stable multivibrator of said first time measuring circuit, a first rst-pulse deletion circuit coupled to the opposite end of said transmission line, second means coupled to the output of said first first-pulse deletion circuit for passing only said second electric pulse, the output of said second means being applied to the bi-stable multivibrator of each tof the time measuring circuits, a second yfirst-pulse deletion circuit coupled to the output of said Erst first-pulse deletion circuit, third means coupled to the output of said second first-pulse deletion circuit for passing only said third electric pulse, the output of said third means being applied to the bi-stable multivibrator of said second time measuring circuit and a third first-pulse deletion circuit coupled to the output of said second firstpulse deletion circuit, the output of said third first-pulse deletion circuit being applied to the bi-stable multivibrator of said third time measuring circuit.

References Cited in the le of this patent UNITED STATES PATENTS Isaacson lan. 30, 196,2 

1. AN ACOUSTICAL VELOCITY WELL LOGGING SYSTEM COMPRISING AN ELONGATED TOOL ADAPTED TO BE PASSED THROUGH THE BOREHOLE OF A WELL, SAID TOOL HAVING FIRST, SECOND AND THIRD TRANSDUCERS POSITIONED IN FIXED SPACED APART RELATIONSHIP IN SAID TOOL, SAID TRANSDUCERS BEING MOUNTED FOR ACOUSTIC COMMUNICATION WITH MATERIAL INCLUDING A SUBSURFACE FORMATION OPPOSITE SAID TOOL, MEANS FOR TRANSMITTING ACOUSTIC PULSES AT PREDETERMINED TIME INTERVALS THROUGH A SUBSURFACE FORMATION OPPOSITE SAID TOOL, MEANS FOR PRODUCING A FIRST ELECTRIC PULSE AT THE OCCURRENCE OF A GIVEN ONE OF SAID ACOUSTIC PULSES AT SAID FIRST TRANSDUCER, MEANS FOR PRODUCING A SECOND ELECTRIC PULSE UPON THE ARRIVAL OF SAID GIVEN ACOUSTIC PULSE AT SAID SECOND TRANSDUCER, MEANS FOR PRODUCING A THIRD ELECTRIC PULSE UPON THE ARRIVAL OF SAID GIVEN ACOUSTIC PULSE AT SAID THIRD TRANSDUCER, A SINGLE INSULATED CONDUCTOR, MEANS FOR APPLYING SAID FIRST, SECOND AND THIRD ELECTRIC PULSES TO ONE END OF SAID SINGLE CONDUCTOR, FIRST AND SECOND TIME MEASURING CIRCUITS, MEANS COUPLED TO THE OTHER END OF SAID SINGLE INSULATED CONDUCTOR FOR APPLYING A DIFFERENT PAIR SELECTED FROM SAID FIRST, SECOND AND THIRD ELECTRIC PULSES TO EACH OF SAID TIME MEASURING CIRCUITS SO AS TO MEASURE THE TIME INTERVAL BETWEEN THE RESPECTIVE PULSES OF THE SELECTED PAIRS OF SAID ELECTRIC PULSES. 